Microsuspension assemblies for direct access storage devices

ABSTRACT

Embodiments include a method for forming a head suspension assembly. A spacer layer is formed in or on a silicon wafer. A transfer film including an opening defining the shape of a slider support membrane is provided, and the opening is filled with a resin material. The transfer film with the resin material therein is positioned over the silicon wafer so that at least a portion of the resin material is positioned adjacent to the spacer layer. The resin material is baked to form a glassy carbon material. The spacer layer is etched to form a trench in the silicon wafer adjacent to the glassy carbon material, and a slider is positioned on the glassy carbon material over the trench.

This is a divisional of U.S. application Ser. No. 10/047,229, filed Jan.14, 2002 now U.S. Pat. No. 6,725,526, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to disk drivesystems and to microsuspension structures which support read/writerecording heads within the systems.

DESCRIPTION OF RELATED ART

Direct access storage devices typically include a rotatable magneticdisk having concentric data tracks defined for storing data, and amagnetic recording head or transducer for reading data from and writingdata to the various data tracks. In typical disk drive systems, a stackof one or more magnetic disks is mounted over a spindle on a drivemotor. The system also includes a head actuator including a headsuspension assembly for supporting and moving the magnetic recordinghead relative to the disk surfaces, and electronic circuitry forprocessing signals to implement various functions of the disk drive. Thehead suspension assembly typically provides an arm-like structure. Thesuspension assembly supports the head close to the surface of the diskas the disk rotates. The magnetic head is carried on a slider having anair bearing surface which is positioned during operation adjacent to thedata surface of the disk and usually separated from the surface of thedisk by a cushion of air generated by the rotating disk. The terms“head” and “slider” are sometimes both used to refer to the sliderhaving a head attached thereon. The slider design affects theefficiency, density, speed and accuracy with which the data can be readand written to the disk.

The suspension assembly connects the slider to a rotary or linearactuator which operates to move the suspension assembly to position themagnetic head directly adjacent to the desired track location on thedisk. Suspension assemblies are typically shaped as an elongated loadbeam adapted to be connected to an actuator arm at one end. The otherend includes a flexure member on which the slider is positioned. Theflexure member is designed to permit an amount of spring-type movementof the slider, while also being rigid in a lateral direction to minimizeundesirable side to side motion of the slider. Steel has been used as asuspension assembly material due to its mechanical properties andbecause it can be milled into fine structures. However, as magneticheads and sliders become smaller and lighter, smaller suspensionassemblies with a higher width to thickness ratio are needed. However,materials such as steel have a limited strength to mass ratio.

Silicon has been proposed as a magnetic head suspension assemblymaterial. The use of silicon for the entire head suspension assembly hascertain advantages such as the ability to form certain electricalcomponents directly on the assembly, and the ability to utilize certainprocessing methods similar to those used for integrated circuitmanufacture. U.S. Pat. No. 5,711,063 describes a process for forming amagnetic head assembly in which silicon is cut into a suspensionassembly shape and then masked and etched to remove additional siliconand to form structures such as a plateau on the head suspensionassembly. However, micromachining silicon to form such structures istime consuming and complex and such silicon structures may lack thenecessary mechanical properties needed for the suspension assembly.

SUMMARY

Certain embodiments relate to suspension structures for a magneticrecording head and methods for producing such suspension structures. Thesuspension arm contains a membrane structure that primarily supports thehead structure. Other properties include the option to electricallyconduct or isolate conductive paths to and from the head via thesuspension arm.

Embodiments include a head suspension assembly including a suspensionarm having a trench formed therein. The head suspension assembly alsoincludes a membrane positioned on the suspension arm and adapted tosupport a slider thereon, wherein at least a portion of the membrane ispositioned adjacent to the trench. In one aspect of certain embodiments,the suspension arm is silicon and the membrane is a glassy carbonmaterial.

Embodiments also include a method for forming a head suspensionassembly. The method includes forming a spacer layer in a portion of asubstrate. The method also includes forming a transfer film having amold of a suspension membrane therein, and filling the mold of thesuspension membrane with a layer of material. The transfer filmincluding the mold of the suspension membrane filled with the layer ofmaterial is positioned over the substrate. The layer of material isbaked to densify at least a portion of the layer of material. The spacerlayer is removed from the substrate to form a cavity extending adistance into the substrate, and the baked layer of material is at leastpartially positioned over the cavity.

Embodiments also include a method for forming a head suspensionassembly, including forming a spacer layer in or on a silicon substrate.A transfer film having an opening defining the shape of a slider supportmembrane is provided, and the opening is filled with a resin material.The transfer film with the resin material therein is positioned incontact with the silicon substrate so that at least a portion of theresin material is positioned adjacent to the spacer layer. The resinmaterial is baked to form a glassy carbon material, and the spacer layeris removed to form a cavity in the silicon substrate surface adjacent tothe glassy carbon material.

Embodiments also include a method for forming a head suspensionassembly, including forming a sacrificial layer in or on a portion of asubstrate. A transfer film is formed across the substrate. A patternedphotoresist layer is formed on top of the transfer film. The method alsoincludes transferring the image of patterned photoresist layer throughthe transfer film, and removing the patterned photoresist layer. Inaddition, the sacrificial layer is removed to form a cavity extending adistance into the substrate.

Embodiments also include a disk drive for reading and writing disks. Thedisk drive includes at least one disk and read/write head adapted toread from and write to the disk. The disk drive also includes a slideronto which the read/write head is provided. The disk drive also includesa suspension assembly adapted to support the slider, wherein thesuspension assembly includes a membrane positioned on a support armhaving a cavity therein, and the membrane is positioned to extendadjacent the cavity. The disk drive also includes a rotatable hub formounting the disk.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the invention are described with reference to theaccompanying drawings which, for illustrative purposes, are schematicand not necessarily drawn to scale.

FIG. 1 illustrates a top view of a wafer from which a plurality ofsuspension assemblies may be formed and illustrates a sacrificial layerformed on the wafer during a manufacturing step in accordance with anembodiment of the present invention.

FIGS. 2 a and 2 b illustrate a top view and side view of a singlesuspension assembly illustrating the sacrificial layer shown in FIG. 1.

FIG. 3 illustrates a side view of a master structure including aninverse image of a membrane structure, and a molding or transfer film onthe master structure during a manufacturing step in accordance with anembodiment of the present invention.

FIG. 4 illustrates the transfer film of FIG. 3 including a resinmaterial in the opening in during a manufacturing step in accordancewith an embodiment of the present invention.

FIG. 5( a) illustrates the transfer film of FIG. 4 with the resinmaterial therein positioned on the suspension assembly during amanufacturing step in accordance with an embodiment of the presentinvention.

FIG. 5( b) illustrates a cross-sectional view of an embodiment along theline A–A′ of FIG. 5( a).

FIG. 6 illustrates the resin material positioned on the suspensionassembly in accordance with an embodiment of the present invention.

FIG. 7( a) illustrates a membrane formed on the suspension assemblyafter a baking step in accordance with an embodiment of the presentinvention.

FIG. 7( b) illustrates the suspension assembly after the sacrificiallayer has been removed in accordance with an embodiment of the presentinvention.

FIG. 8( a) illustrates the suspension assembly including a sliderpositioned thereon in accordance with an embodiment of the presentinvention.

FIG. 8( b) illustrates circuitry and wiring formed in and/or on thesuspension assembly in accordance with an embodiment of the presentinvention.

FIG. 9 illustrates a top view of a suspension assembly including amembrane structure on which a slider can be positioned in accordancewith an embodiment of the present invention.

FIG. 10( a) illustrates a top view of a suspension assembly including amembrane structure on which a slider can be positioned in accordancewith an embodiment of the present invention.

FIGS. 10( b) and 10(c) illustrate top views of a suspension assemblyincluding a membrane structure on which a slider can be positioned andwiring lines in accordance with embodiments of the present invention.

FIGS. 11–12 illustrate the formation of a sacrificial layer and membranestructure in accordance with embodiments of the present invention.

FIG. 13 illustrates a disk drive system in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION

Preferred embodiments of the present invention are described withreference to FIGS. 1–13. While this invention is described in terms ofthe best mode for achieving this invention's objectives, it will beappreciated by those skilled in the art that variations may beaccomplished in view of these teachings without deviating from thespirit or scope of the invention.

Certain embodiments relate to a structure that includes a thin membranethat acts as an intermediate structure between a suspension arm and anair-bearing slider body. The structure may preferably be formed from aglassy carbon material. In certain embodiments, the structure may bemass produced. The structure may include one or more of the followingfeatures: (1) it is independent of the suspension arm material, (2) itallows for a predetermined amount of pitch and roll compliance whilemaintaining its structural integrity, (3) it may be designed to includemicrosprings or integrated circuits therein, (4) it can be produced inan efficient and inexpensive manner, and (5) it can be handled withoutexposing the air bearing slider bond to stress damage.

Certain embodiments relate to a structure formed on a substrate usingmicro-contact printing with a carbon-rich resin filled over asacrificial layer on a silicon suspension arm. Through a heat treatmentprocess at elevated temperature, the resin is transformed into aglass-carbon alloy material that is less stiff and has a lower massrelative to the underlying silicon suspension arm. A process for forminga glass-carbon alloy material is described in an article entitled“Fabrication of glassy carbon microstructures by soft lithography,” inSensors and Actuators, A72 (1999) at pages 125–139, by authorsSchueller, Brittain, and Whitesides, which is hereby incorporated byreference in its entirety.

Preferred embodiments include a suspension assembly and itsmanufacturing process including the formation of a thin micromechanicalmembrane on an arm structure using a contact deposition process. Asillustrated in FIG. 1, a suspension assembly structure may include abase formed from, for example, a silicon wafer 8 wherein a plurality ofsuspension arms 10 (as indicated by the dashed lines) are masked on thewafer 8. A sacrificial layer 12 is then formed on or embedded in thesilicon wafer 8. The sacrificial layer 12 may be formed using a methodsuch as, for example, etching and filling a trench or cavity in thesilicon wafer 8 with a material such as, for example, copper, in adamascene process. This will leave the silicon wafer 8 with a surfacehaving an in-laid copper trench (sacrificial layer 12). The depth andlength of the trench may define a maximum deflection of the membrane andminimum length of the membrane. The silicon wafer surface and coppertrench preferably have a planar surface. FIGS. 2( a) and 2(b) illustratetop and side views of a single suspension arm 10 having a sacrificiallayer 12 in the trench. The maximum deflection of the membrane in thisembodiment will be limited by the depth D of the trench holding thesacrificial layer 12, as seen in FIG. 2( b). As seen in FIG. 2( b), thesuspension arm 10 may have a thickness Z, where D is less than or equalto Z. In addition, a membrane embodiment as described below may beformed to have a length greater than length L of the trench holding thesacrificial layer 12, as seen in FIG. 2( a). In addition, the suspensionarm 10 may have a width Y and the sacrificial layer 12 may have a widthW, as seen in FIG. 2( a). In preferred embodiments W is less than orequal to Y.

The formation of a polymer-resin contact layer is described next. Aseparate master structure such as a silicon wafer is provided with theetched inverse image of the membrane structure to be formed. The mastermay be formed by depositing, patterning and exposing a photoresist layeron the master wafer. The master wafer can be used to create polymerresin-transfer films. A layer of a material, for example, elastomericpolydimethylsiloxane, also known as PDMS (SYLGARD 184, Dow Corning) isformed on the master (for example, by a spin-on process) and conforms tothe surface that includes the inverse image of the membrane structure.The PDMS is cured (for example, at 60° C. for 1 hour) to cross link thepolymer and removed from the master wafer. The PDMS may shrink duringthe curing step. The removal may be carried out, for example, by peelingthe PDMS from the master. A replica (transfer film 14) of the mastersilicon surface is thus formed. FIG. 3 shows a side view of a master 13including an inverse image 18, and the transfer film 14 of the PDMSmaterial. Other embodiments may use materials other than PDMS, such asother polymeric materials, for example.

As illustrated in FIG. 4, the transfer film 14 is removed from themaster 13 and a resin-polymer film 16 is then coated on the transferfilm 14 to fill the image of the membrane structure 18 in the transferfilm 14. Methods which may be used for coating the resin-polymerincluding, but are not limited to dipping, pouring, spraying, andspin-on processes as known in the art. The resin-polymer film 16 is aprecursor material that upon processing will form a glassy carbonmaterial such as that described in the article “Fabrication of glassycarbon microstructures by soft lithography,” in Sensors and Actuators,A72 (1999) at pages 125–139, by authors Schueller, Brittain, andWhitesides, which as noted earlier, is hereby incorporated by referencein its entirety. A variety of polymeric precursor materials including,for example, polyvinyl chloride, polyvinylidene chloride,polyacrylonitrile, cellulose, resins of phenol-formaldehyde, andpolyfurfuryl alcohol may be used. One specific example includes afurfuryl alcohol-modified phenolic resin (FURCARB LP-520, from Q.O.Chemicals, West Lafayette, Ind.). A catalyst solution (for example, ZnClin H₂O) may be included to assist in the curing of the resin-polymermaterial. Excess material is removed and the transfer film 14 with theresin-polymer 16 is positioned on the silicon suspension arm 10 havingthe copper sacrificial layer 12 as illustrated in FIG. 5( a). Ifdesired, an adhesion layer may be formed on the silicon so that theresin-polymer and silicon form a strong bond. FIG. 5( b) illustrates anembodiment in cross section along the line A–A′ of FIG. 5( a), includingan optional layer 17 which may act as an adhesion layer between thesilicon suspension arm 10 and the resin-polymer 16. Such an adhesionlayer 17, if used, may be formed from a variety of materials, including,but not limited to Ta, Ti, TiN, and HMDS.

The resin-polymer material 16 may then be carefully cured to cross-linkthe polymer, for example, by slowly raising the temperature from about60° C. to 150° C. over about one hour. The slow increase in temperatureis carried out to inhibit the formation of stresses leading tomechanical deformation of the structure. The PDMS transfer film 14 maythen be removed, leaving the cured resin-polymer 16 on the suspensionarm 10 over the copper sacrificial layer 12, as illustrated in FIG. 6.The PDMS transfer film 14 may be removed using a variety of methods, forexample, peeling back the film, chemically removing the film, andburning off the film during a high temperature processing step. Ifdesired, the resin-polymer may be degassed prior to transfer to thesubstrate and prior to heating, in order to remove any excess solventand to limit shrinkage of the structure. In certain embodiments, afterthe transfer film with the resin-polymer is transferred to thesubstrate, it is held at room temperature for a time period (such as 12hours, for example), which may help reduce residual stresses.

A high temperature baking process is applied (preferably in a noble gas)to cross link and carbonize the carbon-rich resin 16. When using afurfuryl alcohol-modified phenolic resin as the carbon-rich resin 16,the baking process may be carried out, for example, in argon attemperatures up to about 1100° C. One preferred embodiment utilizes atemperature of about 900° C. It is believed that the resin polymer istransformed into glassy carbon occurs by about 800° C. The baking causesa densification of the structure, in particular as the resin is beingtransformed into the glassy carbon. Preferably the shrinkage is limitedto preserve the shape of the structure. The use of resins with a highcarbon yield is preferred in order to minimize shrinkage. One or morecleaning steps may also be incorporated into the process (at varioustimes) to remove left over molding materials, polymer materials, orother undesirable materials on the surface of the suspension arm 10. Inpreferred embodiments the glass carbon structure is relatively inert andelectrically conductive. The microstructure generally includes randomlyoriented crystallites in a glassy matrix. Glassy carbon is sometimesknown in the art as vitreous carbon.

In the event a high temperature process is used to cure the materialthat will eventually become the membrane structure, the sacrificialmaterial preferably has a melting point below the bake temperature

After the high temperature baking process, a glassy carbon 20 (formedfrom the resin 16) is positioned over or adjacent to the sacrificialcopper layer 12 on the silicon arm 10 as illustrated in FIG. 7( a). Theterm adjacent as used above refers to at least a portion of the membrane20 being positioned either over or under or next to the sacrificialcopper layer, depending on the orientation of the device. Thesacrificial copper layer 12 that is located beneath the membrane 20 maybe removed, leaving a cavity 22 under the membrane 20 as illustrated inFIG. 7( b). This may be carried out, for example, by dipping the waferinto a copper etchant. The carbon-glass membrane is chemically resistantto the etching solution and will not be significantly removed while thesacrificial copper is etched. A slider 24 may be positioned on themembrane 20 as illustrated in FIG. 8( a). FIG. 8( b) illustrates thesuspension arm 10 including in-line circuitry such as circuit 31 andwiring 33 extending on and/or in the surface of the suspension arm 10 toconnect to the membrane 20 for communication to and from the slider 24.

Other materials to form the membrane that may be utilized are spin-onglasses and/or Polysilsesquioxones (e.g. poly(methylsilsesquioxone) orMSSQ) which, upon annealing, curing, or exposure to a oxygen containingplasma, transforms into a crosslinked glass-containing matrix materialthat may include silica. These materials can be applied to across awafer and crosslinked in the spaces created within a patternedphoto-resist layer. Common catalysts to cure such materials may includedibutylindiacetate, zinc acetate, or zinc 2-ethylhexanoate.

An alternate process to pattern a polysilsesquioxone (e.g., MSSQ) layeris to apply a layer to a wafer with a pre-patterned sacrificialstructure such as shown in FIG. 1. The MSSQ layer is then cured,crosslinked or oxidized. A photoresist layer is patterned on top of theMSSQ and the pattern is transferred through the MSSQ using afluorine-containing plasma. The photoresist layer is removed, leaving astructure on the wafer having a cross-section that is similar to thatshown in FIG. 6. The cured resin 16 using this process will be a curedsilica-containing matrix or polymer.

A variety of membrane 20 designs may be utilized, including, but notlimited to those having arms which may act as springs. FIG. 9illustrates top view of a suspension arm 10 having a cavity 22 thereinand a membrane 20 extending adjacent (and across) the cavity, whereinthe membrane 20 includes arms 26 that make several turns and thenconnect to a central portion 28 on which a slider may be positioned.FIG. 10( a) illustrates another top view of a design in which the arms26 extend straight across the cavity 22. Many other designs are alsopossible. The designs should be selected to provide for an appropriateamount flexibility and stiffness in the desired direction. In certainembodiments, the cavity 22 over which the membrane 20 extends does notextend all the way across the suspension arm 10. In such embodiments, asshown in FIGS. 10( b) and 10(c), the cavity 22 extends across thesuspension arm 10 and ends at a location spaced from the sides 35, 37 ofthe suspension arm 10. If desired, wiring lines 33 may extend on one orboth sides of the membrane 20 adjacent to the sides 35 and 37 and evenextend to a position near to the end 39 of the suspension arm andconnect to one or more of the arms 26 of the membrane 20. FIG. 10( b)illustrates wiring 33 connecting to the arms 26 of the membrane 20. Onewiring portion 33 extends close to suspension arm 10 side surface 35prior to connecting to two arm portions 26 of the membrane. FIG. 10( c)illustrates wiring lines 33 extending very close to sides 35 and 37 andalso shows a single wiring line 33 connected to each membrane arm 26.

While certain embodiments include a suspension assembly having a siliconarm and a glassy carbon membrane thereon, it is also possible to use avariety of other materials for both the arm and the membrane. Inaddition, in embodiments utilizing a sacrificial layer, a variety ofmaterials may be used as the sacrificial material. The size and shape ofthe sacrificial layer may also be varied. In another embodimentillustrated in FIG. 11, a sacrificial layer 12 is formed on the surfaceof the suspension arm 10 instead of in a trench in the suspension arm asdescribed earlier (FIG. 2( b)). The sacrificial layer 12 may be formedin a variety of shapes, for example, a box-like shape as illustrated inFIG. 11( a) and a rounded shape as illustrated in FIG. 11( b). Amembrane 20 may be formed to extend over at least a portion of thesacrificial layer 12 in a manner such as that described earlier. Thesacrificial layer 12 may be removed to leave cavity 22, and a read/writehead 24 may be attached to the membrane 20, as illustrated in FIGS. 12(a) and 12(b).

FIG. 13 illustrates portions of a disk drive system 40 according to anembodiment of the present invention. The system includes one or moremagnetic disks 44 stacked above one another. The disks 44 may beconventional particulate or thin film recording disks, which are capableof storing digital data in concentric tracks. Both sides of the disks 44may be available for storage. The disks 44 are mounted to a spindle 46.The spindle 46 is attached to a spindle motor, which rotates the spindle46 and the disks 44 to provide read/write access to the various portionsof the concentric tracks on the disks.

The disk drive system 40 also includes an actuator assembly 48 includingvoice coil motor assembly 50, which controls a head arm assembly whichmay include a positioner arm 52 and a suspension arm 10. The positionerarm 52 further includes a pivot 54 around which the positioner arm 52moves. The suspension arm 10 may have a variety of geometries, and, asdescribed above, may be formed from silicon and have in-line circuitry,if desired. The suspension arm 10 may support a slider and read/writehead 24. Although only one slider and read/write head 24 is shown, itwill be recognized that the disk drive assembly 10 may include aread/write head for each side of each disk 44 included in the drive.

The disk drive system 40 may further include read/write chip 56. As iswell known in the art, the read/write chip 56 cooperates with theread/write head 24 to read data from and write data to the disks 44. Aflexible printed circuit member may 58 carry digital signals between thechip 56 and the actuator assembly 48.

It will, of course, be understood that modifications of the presentinvention, in its various aspects, will be apparent to those skilled inthe art. Other embodiments are possible, their specific featuresdepending upon the particular application. The scope of the inventionshould not be limited by the particular embodiments described herein.

1. A head suspension assembly comprising: a suspension arm having atrench formed therein; and a membrane positioned on the suspension armand adapted to support a slider thereon, wherein at least a portion ofthe membrane is positioned adjacent to the trench, and a sliderpositioned on the membrane over the trench.
 2. A head suspensionassembly as in claim 1, wherein the suspension arm and the membrane areformed from materials having different compositions.
 3. A headsuspension assembly as in claim 2, wherein the suspension arm is formedfrom silicon.
 4. A head suspension assembly as in claim 2, wherein themembrane is formed from a material including carbon.
 5. A headsuspension assembly as in claim 1, wherein the membrane comprises aglassy carbon material.
 6. A head suspension assembly as in claim 1,wherein the suspension arm is formed from a silicon wafer and themembrane comprises a glassy carbon material.
 7. A head suspensionassembly as in claim 1, wherein the membrane is formed from anelectrically conductive material.
 8. A head suspension assembly as inclaim 1, further comprising at least one wiring line electricallycoupled to slider positioned on the membrane, wherein at least a portionof one wiring line is positioned so that the wiring line extends atleast one of (a) into the suspension arm to a depth, and (b) on thesurface of the suspension arm.
 9. A head suspension assembly comprising:a suspension arm having a trench formed therein; and a membranepositioned on the suspension arm and adapted to support a sliderthereon, wherein at least a portion of the membrane is positionedadjacent to the trench, and wherein the membrane extends across thetrench.
 10. A head suspension assembly as in claim 9, wherein thesuspension arm is formed from a silicon wafer and the membrane comprisesa glassy carbon material.
 11. A disk drive for reading and writingdisks, the disk drive including a head suspension assembly, the diskdrive comprising: at least one disk; a rotatable hub for mounting thedisk; a read/write head adapted to read from and write to the disk; aslider onto which the read/write head is provided; and a suspensionassembly adapted to support the slider, the suspension assemblyincluding a suspension arm defining a cavity, and a membrane positionedon the suspension arm and adapted to support the slider thereon, whereinat least a portion of the membrane is configured to deflect into thecavity when a suitable force is applied to the read/write head.
 12. Adisk drive as in claim 11, wherein the membrane comprises a glassycarbon material and the suspension arm comprises silicon.
 13. A diskdrive as in claim 11, wherein the membrane extends over a portion of thecavity.
 14. A disk drive as in claim 11, wherein the membrane extendsacross the cavity.
 15. A head suspension assembly comprising: asuspension arm having a cavity formed therein; and a membrane positionedon the suspension arm and adapted to support a slider thereon, whereinat least a portion of the membrane is configured to deflect into thecavity when a suitable force is applied to the membrane.
 16. A headsuspension assembly as in claim 15, wherein the suspension arm and themembrane are formed from materials having different compositions.
 17. Ahead suspension assembly as in claim 15, wherein the membrane comprisesa glassy carbon material.
 18. A head suspension assembly as in claim 15,wherein the suspension arm is formed from silicon.
 19. A head suspensionassembly as in claim 15, wherein the membrane extends across the cavity.20. A head suspension assembly as in claim 15, further comprising aslider positioned on the membrane.